This relates to the maintenance and testing of communication lines and, in particular, to the maintenance and testing of conventional telephone lines.
In the course of testing telephone lines it is generally desireable to have the capacity to detect whether the line is currently in use. Line usage, in this context, includes subscriber conversations as well as other communications applications. Because many tests of the performance of the telephone line disrupt such usage, it is advantageous to test only those lines that are not in use at the time the test begins. Thus, the capability to detect speech or tone signalling on a telecommunication line can be quite useful. In addition, although a line may appear to be in use, it may actually be off-hook, or central office equipment may have failed to release it after actual use has terminated. Having the ability to detect speech and tones, therefor, permits a busy condition signal to be tested for validity.